It took scientists more than a decade and about $1bn to unlock the secrets of the human genome. Now consumers are being offered the chance to get a personalised copy of their DNA - for £500 and a vial full of spit.

A web-based testing service launches in Europe today after being available in the US since November, offering insights into your genetic background and likelihood of getting an inherited disease.

Subscribers to 23andMe - it focuses on 23 pairs of chromosomes - are sent a home test kit comprising a plastic tube to be filled with saliva. This is sent to a laboratory for decoding, and about four weeks later users are given password-protected access to their personal genetic analysis on the website. Tests will be able to say whether you have an increased risk of diseases such as multiple sclerosis, diabetes and certain cancers, and also provides less useful information such as the type of earwax a person has.

The service is likely to provoke controversy in the UK, where authorities have warned that genetic tests are often meaningless yet can provoke needless anxiety among those who take them. Last month the Human Genetics Commission condemned them as a dangerous waste of money and called for regulations to control their marketing.

Founders of the scheme Anne Wojcicki - wife of Google co-founder Sergey Brin - and Linda Avey, say it has been well received in the US and "we're seeing very few problems", in spite of ethical concerns that have been raised. What people receive, they say, is some fascinating if incomplete information about themselves and their family - and no dramatic revelations about hereditary diseases that will kill them before they are 40.

The analysis does not look for the single genes that predict Huntingdon's disease or an aggressive form of breast cancer. Instead it focuses on sequences called SNPS (single nucelotide polymorphisms) on 23 pairs of chromosomes. Some of these SNPS have been linked to raised risks of particular diseases, but in most cases lifestyle and environment play as big or a bigger part.

"People have found the information was not worrying," says Wojcicki.

In the UK, however, the Human Genetics Commission's report on direct-to-consumer tests warned that neither exact nor complete knowledge of what differences in the chromosome pairs mean exist yet. "Our advice to the public is that with many of the tests currently on the market people are wasting their money," said Dr Christine Patch, co-author of the report. "At the moment the science is simply not strong enough. The tests could be positively harmful if the results caused unnecessary anxiety or gave false reassurance."

Dr Helen Wallace, director of the pressure group Gene Watch, is equally concerned. "Our main concern is that the human genome is set to become a massive marketing scam," she said, adding that special diet foods and pills had been promoted on the back of tests. "Genetic tests like these are not regulated and the science is still poorly understood - so there is a real danger people could be misled about their health."

The information could eventually lead to problems with insurance. At the moment there is a voluntary moratorium, brokered by the government, on the use of genetic information in deciding insurance premiums, but that expires in 2011. After that it is possible that people who have been told about their vulnerability to disease may be required to disclose this when applying for insurance.

Wojcicki and Avey argue that those who want to know about their genetic make-up should be treated as adults and given the data, together with careful explanations of what it means. The website offers a calculator to assess your increased genetic risk, but also caveats and advice.

Even so, it is not for the fainthearted. Among the conditions linked to some SNPs are certain types of cancer and incurable multiple sclerosis. When Wojcicki took the test she discovered she was a carrier of Bloom's disease - a genetic mutation that affects one in 100 Jews of eastern European descent. But that, in her view, is useful information. Wojcicki and her husband are hoping to have children, but two carriers have a 25% chance of a child with the disease, which has physical characteristics including short stature and an increased likelihood of cancer. Fortunately, Brin was in the clear.

Wojcicki claims that understanding your genes is empowering. If she found she had a raised likelihood of type two (obesity-linked) diabetes, she would watch her diet. The real fascination for both women is in tracking back their genetic ancestry and they have talked family members into being tested too, so they can compare genes.

The website allows people to compare their genetic information. You have to send a request to somebody on the site and get permission if you want to have a look at their SNPS. "I have a friend," says Wojcicki, "and we have a tiny bit of shared DNA on chromosome 3 and chromosome 7. It's a little tiny piece. Yet I'm of Polish Catholic and Russian Jewish descent and he's from Beirut."

FAQ What it tells you

What do they test for?

The company scans for genetic variations in DNA. Some of these are linked to an increased risk of disease, while others say something about the body's make up. Among the medical risks the test looks for are breast cancer, Crohn's disease, heart attack, multiple sclerosis, obesity and diabetes. Other genetic variations reveal more obscure details about physiology - for example, the kind of muscle fibres you have, your bitter taste perception, and even your type of earwax.

How reliable is it?

The tests cannot diagnose, or predict with any confidence, a person's risk of getting disease in the future. The reason is that the genetic markers tested for account for only a small fraction of overall risk. In many cases tests look at just one or two markers for a disease, but there could be tens of others that are not yet known. One genetic marker 23andMe looks at to assess the risk for multiple sclerosis is called IL7RA, but it accounts for less than 0.2% of the risk of developing the disease. Other markers have a greater influence. Two copies of the FTO marker, or "fatso" as it has become known, increases risk of obesity by 70%. Last month the government's genetics advisers published a report warning customers to be cautious in interpreting results from genetic tests. It also cautioned that some might take "good" test results as a licence to binge and exercise less.